How To Install Roofing Felt
Once you understand what it does, and you know which one you need, you are ready to lay the underlayment for your roof. But, as with so many other projects, the key lies in the prep work. If you take the time to properly prepare the roof, then laying the felt will be easy. On the flipside, if you rush through the initial steps, the felt installation can be compromised by sloppy oversights such as stray nails.
Check the weather. Ideally, the roof should be done when there is a forecast for several days without a lot of rain.
- The roof decking should be completely clean and dry. Any stray roof tacks, pieces of old felt, or general debris should be cleared off. Running a flat bottom shovel along the roof decking will help you find any stray nails that should be pulled. Wood splinters should also be pulled out for a smooth, clean decking surface. This step is vital to the success of your new roof and must not be shortchanged in any way.
- Before laying roof felt, all rotten decking must be replaced. Drip edges on the eaves, any valley liners and all flashing should be installed before the tar paper is laid.
- Chalk lines should be snapped 33 5/8” above the eave line. After this, lines should be snapped every 34” as you move up the roof. Have a helper ready to assist with this step, and take care to get the lines straight and clean.
Laying the Felt
The roofing felt should be applied in layers that overlap. Start at the bottom of the roofline and work up so any water that gets through the roofing material will shed down the tar paper and will not go under it.
- As you work, the paper can be tacked down in the center so it won’t blow away.
- When you arrive at the rake, the paper should be cut flush with a knife and then adjusted to line up with the chalk line. The overhang to the next strip should be 3/8 inch. The paper should then be nailed in or stapled every three to four inches across. All nails and staples should be placed on the lower half of the paper.
- Where a roll ends and a new one is begun, the two rolls should be overlapped by four inches.
- Valley, ridges and hips should have a 6 inch overlap of paper.
- Paper can be fitted around vent pipes by cutting a slit and then putting it over the pipe.
- Before securing the end of a row, take time to walk the row, smoothing out any rough spots and matching up the snapped chalk lines. Smooth application of the roofing paper will help you achieve a smooth installation of the shingles.
- Be sure the tar paper lies in flat strips that are absolutely smooth. There should be no wrinkles or other spots that could catch moisture and cause problems. The overlap of 3/8” should be followed consistently for a smooth look once the shingles are installed.
Some roofing felts are actually glued down. These applications are ideal for flat roofs or protective surfaces under roof-level decks. These thick layers of roofing felt are installed by heating the back of the felt with a butane torch and then carefully applying it to the roof.
Installing the roofing felt does take care, but can go very quickly. Taking the time to properly prepare the sheathing will make all the difference in how quickly and easily the felt paper is installed. The actual process of putting down the underlayment will be one of the fastest parts of the entire roofing process.
Check the requirements for the roofing material that will go over the felt. Some materials require heavier felt paper.
- Never mount the felt paper on wet sheathing. Mold and mildew will result and you could wind up having to rip off the roof and install a new one. Dry sheathing and felt paper also help ensure a watertight roof in severe climates.
- Strips should always lay flat. Uneven strips and wrinkles can allow dust, moisture and mold to develop.
- Sheathing that gets wet before the roofing material can go on should be allowed to dry thoroughly before continuing. Typically 2 to 3 days will be required for this.
Tools and Supplies
A tape measure and chalk line are needed for snapping the guidelines on the roof.
Two or more people are required to help roll out and straighten the paper during the process.
A nail gun can be used to quickly install some nails to the roofing paper won’t slide around. Follow manufacturers’ instructions when choosing nails.